There is a method of creating NC data for machining in accordance with the profile of a model using model surface data digitized while tracing is executed.
FIG. 4 is an explanatory view in which surface data of a model MDL are digitized by X-Z two-way surface tracing. This involves moving a stylus STL along the X axis at a predetermined tracing velocity, allowing the stylus to move up and down along the model MDL in the direction of the Z axis, and storing three-dimensional position data indicative of stylus position every predetermined time. When the boundary of a tracing region TRR is reached, a predetermined amount of pick-feed is performed in the direction of the Y axis, after which surface tracing is similarly executed in an opposite x-axis direction. During this surface tracing, the position of the stylus STL is monitored, the resulting position data are accepted and the surface of the model MDL is digitized. The surface data are subsequently employed to create NC data.
For cases in which a workpiece is subjected to roughing-out machining by a tool 21 of a predetermined diameter using a plurality of digitized point sequence path data a in the prior art, a method has already been put into practical use in which NC data for rough machining are created while skipping a number of point sequence paths at equal intervals. For example, letting Ll .about.L7 represent a plurality of digitized point sequence paths, as shown in FIG. 5, Ll, L4 and L7 are adopted as the cutting paths for rough machining, with two point sequence paths (L2, L3 or L5, L6) being skipped between each adopted path.
After rough machining tool 21 performs machining from right to left along, the point sequence path Ll, a pick-feed is performed in the Y-axis direction and then machining is carried out from left to right along the next point sequence path L4. This means that the region actually machined by the rough machining tool 21 by movement along the latter L4 path is solely the portion (the shaded portion) indicated by A, with the remaining portion being a region already cut, namely a non-cutting region E overlapping the previously cut path.
Accordingly, if the number of skipped point sequence paths is designated improperly, the non-cutting region E will be larger than the actually cut region A. In other words, the overlap of the previously cut path consumes too much time and efficiency suffers.
An object of the present invention is to provide a method of creating NC data for rough machining in which, when a workpiece is subjected to roughing-out machining by a tool of a predetermined radius using a plurality of digitized point sequence path data, non-cutting regions are reduced so that highly efficient roughing-out machining can be performed.